Positive electrode material, preparation method thereof, positive electrode sheet and sodium ion battery

Abstract

The application provides a positive electrode material, a preparation method of the positive electrode material, a positive electrode sheet and a sodium ion battery. x Mn 1‑x / 2 V(PO4) 3‑x / 3N x , wherein 0.001<=x<=0.05; M is Li and / or K, and N is selected from one or more of F, Cl, Br and I. The application realizes the regulation of the particle morphology size of the positive electrode material, promotes the significant improvement of the comprehensive performance of the specific capacity, rate performance, cycle stability and compaction density of the positive electrode material, and the like, while improving the intrinsic conductivity and structural stability of the positive electrode material in a larger range, by synchronously introducing specific types and contents of anions and cations in the polyanionic phosphate positive electrode active material.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion batteries, in particular to a positive electrode material, a preparation method thereof, a positive electrode sheet and a sodium ion battery. BACKGROUND

[0002] Sodium ion batteries are expected to become a good substitute for lithium ion batteries due to the abundance of sodium resources, low price and similar electrochemical behavior to lithium. Sodium ion batteries are considered a promising alternative solution for new energy vehicle battery technology due to their cost-effectiveness, environmental friendliness, safety, temperature adaptability, fast charging capability and long cycle life. With the advancement of technology, sodium ion batteries are expected to become one of the mainstream battery technologies for new energy vehicles in the coming years, providing more durable and safer power for electric vehicles. Among them, the positive electrode, as an important component of the sodium ion battery, has an important influence on various indicators of the overall battery. Common sodium ion positive electrode materials such as layered transition metal oxides, prussian blue compounds and polyanion compounds all have the shortcomings of low specific energy and poor cycle stability, which will hinder commercial development and practical application. Therefore, it is urgent to develop sodium ion battery positive electrode materials with excellent electrochemical performance to meet actual needs.

[0003] NASICON-type phosphates in polyanion compounds have the advantages of structural stability, high ionic conductivity and high voltage platform, and have become the focus of development of sodium ion battery positive electrode materials. Among them, sodium vanadium manganese phosphate [Na4VMn(PO4)3] material has attracted much attention due to its high specific capacity (117 mAh·g -1 ). However, the material has poor electronic conductivity and undergoes irreversible phase transition during charging and discharging, causing rapid capacity decline, resulting in unsatisfactory cycle stability and rate performance. In order to improve the electrochemical performance of Na4VMn(PO4)3, researchers have adopted ion doping technology to overcome the inherent defects of the material. In recent years, some studies have shown that cation doping can effectively inhibit the lattice distortion of Na4VMn(PO4)3 material caused by the Jahn-Teller effect of Mn 3+ , and can increase the vacancy concentration of Na + , thereby enhancing its ion diffusion capacity; in addition, anion doping can also cause defects in the lattice of Na4VMn(PO4)3 material, thereby widening the transmission channel of sodium ions and improving the stability of the material.

[0004] In summary, the use of cation or anion doping alone can overcome the inherent defects of the Na4VMn(PO4)3 material to some extent, and is conducive to improving its intrinsic conductivity. However, whether the NASICON-type phosphate crystal is subjected to cation doping alone or anion doping alone, the material lattice structure will be unstable, thereby affecting the mechanical properties and thermal stability of the material. Moreover, up to now, there is still a lack of relevant research on simultaneously doping the Na4VMn(PO4)3 material with cations and anions, and especially little is known about whether cations and anions can be synergistically doped.

[0005] Therefore, how to realize the co-doping of cations and anions in the polyanion-type phosphate positive electrode active material of the sodium ion battery to make the polyanion-type phosphate positive electrode active material have more superior electrochemical performance is one of the important technical problems to be solved in the field. SUMMARY

[0006] The main purpose of the present application is to provide a positive electrode material, a preparation method thereof, a positive electrode sheet and a sodium ion battery, so as to solve the problem of poor electrochemical performance of the polyanion-type phosphate positive electrode active material in the prior art.

[0007] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a positive electrode material, which comprises a composite particle, and the molecular formula of the composite particle is Na4M x Mn 1-x / 2 V(PO4) 3-x / 3 N x , wherein 0.001≤x≤0.05; M is Li and / or K, and N is selected from one or more of F, Cl, Br and I.

[0008] The present application obtains a positive electrode material with particularly excellent electrochemical performance through the co-doping of cations and anions. The introduction of cations and anions can adjust the electronic structure of the positive electrode material, and effectively increase the active sites of the positive electrode material, thereby improving the specific capacity of the positive electrode material. Specifically, compared with other types of cations and anions in the field, the F, Cl, Br and I halogen anions and the Li and / or K alkali metal cations provided by the present application can greatly improve the structural stability of the polyanion-type phosphate material and the diffusion ability of Na + in the polyanion-type phosphate material, so that the positive electrode material has excellent cycle stability and rate performance. At the same time, the co-doping of cations and anions can also realize the regulation of the micro-morphology size of the positive electrode material particles, thereby greatly improving the compaction density of the positive electrode material, so that it has higher energy density in actual application.

[0009] Among them, regarding halogen anions, they have higher electronegativity compared to the commonly used sulfate, phosphate, carbonate and other acid radical ions in the field, can form stronger bonding with the original transition metal ions Mn and V in the positive electrode material, thereby more significantly improving the structural stability and electrochemical performance of the positive electrode material. While Li and / or K alkali metal cations, compared to other cations commonly used in the field, such as Ca 2+ , Mg 2+ , etc., have more suitable ionic radii to more easily embed and de-embed the polyanion phosphate structure, thereby improving the charge and discharge performance of the corresponding battery of the positive electrode material. At the same time, the above ions also exhibit higher electrical conductivity to further optimize the electrochemical performance of the positive electrode material.

[0010] On the basis of the above types of anions and cations, the doping amount of the anions and cations is preferably that the stoichiometric number in the positive electrode material is uniform and all are 0.001≤x≤0.05, thereby being able to more effectively adjust the electronic structure, enhance Na + ion migration and form new active sites, so that the positive electrode material exhibits higher electrochemical performance.

[0011] In particular, in addition to the selection of the above types of anions and cations and the doping amount, more importantly is the coordination relationship between the two doping elements and the polyanion phosphate positive electrode material matrix. The polyanion phosphate positive electrode material itself has a high theoretical specific capacity and good cycle stability, and when the above anions and cations are introduced at a specific doping amount, the electrochemical performance thereof can be further improved. Compared to other types of positive electrode active materials, such as olivine-type phosphates, the polyanion phosphate involved in the present application has better compatibility with the above anions and cations, and ultimately a positive electrode with better electrochemical performance can be obtained. Therefore, the doping of anions and cations can enhance the structural stability, improve the electrical conductivity, promote ion migration, and thereby improve the electrochemical performance of the positive electrode material. This synergistic effect makes the polyanion phosphate positive electrode material have more significant advantages in performance.

[0012] In some embodiments, in the molecular formula of the composite particles, 0.001≤x≤0.01; M is Li and / or K, and N is selected from one or more of F, Br and I.

[0013] In this embodiment, in the molecular formula of the composite particles, 0.001≤x≤0.01, thereby better avoiding the increase of the internal resistance of the positive electrode material and the decrease of the cycle stability due to the destruction of the structure of the positive electrode material. At the same time, it is preferred that M is Li and / or K, and N is selected from one or more of F, Br and I.

[0014] In some embodiments, it is preferred that the molecular formula of the composite particles is Na4M 0.01 Mn 0.995V(PO4) 2.997 N 0.01 , wherein M is Li and / or K, and N is selected from one or more of F, Br and I; or, the molecular formula of the composite particle is Na4M 0.001 Mn 0.9995 V(PO4) 2.9997 N 0.001 , wherein M is Li and / or K, and N is F. Under the above-mentioned optimized molecular structure, the doped anions and cations can better coordinate with each other, and thus the positive electrode material with more superior electrochemical performance can be obtained.

[0015] In some embodiments, considering the changes in the molecular structure and electronic structure of the phosphate positive electrode material caused by the doping of anions and cations, the molecular formula of the composite particle is preferably Na4K 0.01 Mn 0.995 V(PO4) 2.997 F 0.01 , Na4Li 0.01 Mn 0.995 V(PO4) 2.997 F 0.01 , Na4K 0.01 Mn 0.995 V(PO4) 2.997 Br 0.01 , Na4K 0.01 Mn 0.995 V(PO4) 2.997 I 0.01 , Na4K 0.001 Mn 0.9995 V(PO4) 2.9997 F 0.001 , or Na4K 0.05 Mn 0.975 V(PO4) 2.983 F 0.05 , and thus the positive electrode material with better electrochemical performance and more superior stability can be obtained.

[0016] In addition, in order to further improve the stability and electrical conductivity of the positive electrode material, the positive electrode material further comprises a carbon coating layer coated on the outer surface of the composite particle, and the mass fraction of the carbon coating layer is 1% to 5% based on the total weight of the positive electrode material.

[0017] The second aspect of the present application provides a preparation method of a positive electrode material, which comprises: preparing a mixed slurry by mixing a sodium source, a doping element source, a manganese source, a vanadium source and a phosphorus source; and sequentially drying and calcining the mixed slurry to obtain the positive electrode material; wherein the positive electrode material comprises composite particles, and the molecular formula of the composite particles is Na4M x Mn 1-x / 2 V(PO4)3-x / 3N x 0.001<=x<=0.05;M is Li and / or K, N is selected from one or more of F, Cl, Br and I.

[0018] For the above positive electrode material, the application correspondingly provides a preparation method thereof, which is simple in operation and easy to control, can optimize the reaction process to a greater extent, and can prepare the positive electrode material with excellent electrochemical performance at a lower manufacturing cost.

[0019] In some embodiments, the calcination comprises sequentially performing: first-stage calcination at a temperature of 320-370 DEG C for 3-5 h; and second-stage calcination at a temperature of 700-750 DEG C for 7-9 h.

[0020] The application refines the calcination into two stages, thereby helping to better realize the doping of cations and anions, and also better inhibiting the deterioration of the structure of the poly-anion phosphate positive electrode material itself, and enhancing the structural stability and electrochemical performance thereof.

[0021] In order to better protect the structure of the positive electrode material and reduce the introduction and generation of impurities, preferably, the first-stage calcination and the second-stage calcination are both performed under the protection of an inert gas, and more preferably, the inert gas is argon and / or nitrogen. Thus, the positive electrode material with higher electrochemical performance and better stability is obtained, and the specific capacity and long cycle stability of the sodium ion battery prepared therefrom are ultimately higher.

[0022] Further, in order to more quickly and uniformly remove water, reduce material agglomeration, and optimize the microstructure and density of the positive electrode material, the drying is spray drying, and the inlet temperature of the spray drying is 200-250 DEG C, and the outlet temperature is 100-140 DEG C.

[0023] In some embodiments, the doping element source is selected from one or more of potassium fluoride, lithium fluoride, potassium bromide and potassium iodide. The above doping element source can more significantly optimize the molecular structure and electronic structure of the positive electrode material, and does not introduce other impurity elements, so as to more effectively improve the electrochemical performance and structural stability of the positive electrode material.

[0024] In some embodiments, the sodium source is selected from one or more of sodium acetate, sodium carbonate, sodium hydroxide and sodium nitrate; and / or, the phosphorus source is selected from one or more of ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, ammonium phosphate and phosphoric acid. The selection of the sodium source and the phosphorus source has an important influence on the synthesis process and the final performance of the positive electrode material, and by adjusting the types thereof as above, the application can optimize the synthesis conditions of the positive electrode material, and improve the consistency and stability of the material.

[0025] In some embodiments, the manganese source is selected from one or more of manganese acetate tetrahydrate, manganese nitrate, manganese phosphate, and manganese oxalate; and / or, the vanadium source is selected from one or more of ammonium metavanadate, ammonium vanadate, and ammonium sulfate. The selection of the manganese source and the vanadium source can affect the electronic structure and ion diffusion path of the cathode material, and by optimizing them respectively as above, the electronic conductivity and ion diffusion efficiency of the cathode material can be further improved.

[0026] The third aspect of the present application provides a cathode sheet, which comprises the above-mentioned cathode material, or the cathode material prepared by the preparation method of the above-mentioned cathode material. The cathode material provided by the present application has excellent electrochemical performance and stability, so when it is used as an active material of a cathode sheet, the corresponding cathode sheet also has high energy density, long cycle life and excellent electrochemical stability, thereby significantly improving the overall performance of the battery.

[0027] The fourth aspect of the present application provides a sodium ion battery comprising the above-mentioned cathode sheet. The cathode sheet provided by the present application has high energy density and long cycle life due to the presence of the cathode material with excellent electrochemical performance, so when the cathode sheet is applied to a sodium ion battery, the sodium ion battery also has high discharge specific capacity and long cycle stability.

[0028] The present application synchronously introduces specific types and contents of anions and cations into the polyanion phosphate cathode active material, so that the two produce a good synergistic effect, greatly improve the intrinsic conductivity and structural stability of the cathode material, realize the regulation of the particle morphology size of the material, and promote the significant improvement of the comprehensive performance of the material such as specific capacity, rate performance, cycle stability and compaction density, greatly promoting the industrialization application of the material.

[0029] The above description is only a summary of the technical solutions of the present application. In order to more clearly understand the technical means of the present application, the specific embodiments of the present application can be implemented in accordance with the content of the description, and in order to make the above and other purposes, characteristics and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creating laborious work on the basis of these drawings.

[0031] Figure 1 XRD patterns of the cathode materials obtained in Example 1 and Comparative Example 1;

[0032] Figure 2 SEM characterization results of the positive electrode material obtained in Example 1 and Comparative Example 1 are shown in Table 1, wherein Figure 2 (a) and Figure 2 (b) are SEM characterization results of the positive electrode material obtained in Example 1, Figure 2 (c) and Figure 2 (d) are SEM characterization results of the positive electrode material obtained in Comparative Example 1. DETAILED DESCRIPTION

[0033] The embodiments of the technical solutions of the present application will be described in detail below with reference to the accompanying drawings. The following examples are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application; the terms "comprising" and "having", and any variations thereof, as used in the specification and claims and the aforementioned description of the drawings, are intended to cover not exclusively inclusive.

[0035] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0036] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The appearance of the phrase in various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily independent or alternative embodiments to other embodiments. The skilled person in the art explicitly and implicitly understands that the embodiments described herein can be combined with other embodiments.

[0037] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship between the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in this paper generally represents a "or" relationship between the front and rear associated objects.

[0038] As described in the background, the existing polyanionic phosphate positive electrode active material has the problem of poor performance. In order to solve the above technical problems, the first aspect of the present application provides a positive electrode material, which comprises a composite particle, and the molecular formula of the composite particle is Na4M x Mn 1-x / 2 V(PO4) 3-x / 3 N x , wherein 0.001≤x≤0.05; M is Li and / or K, and N is selected from one or more of F, Cl, Br and I.

[0039] The present application obtains a positive electrode material with excellent electrochemical performance by co-doping of anions and cations. The introduction of anions and cations can adjust the electronic structure of the positive electrode material, and effectively increase the active sites of the positive electrode material, thereby improving the specific capacity of the positive electrode material. Specifically, compared with other types of anions and cations in the art, the F, Cl, Br and I halogen anions and the Li and / or K alkali cations provided by the present application can greatly improve the structural stability of the polyanionic phosphate material and the diffusion ability of Na + , so that the positive electrode material has excellent cycle stability and rate performance. At the same time, the co-doping of anions and cations can also realize the regulation of the micro-morphology size of the positive electrode material particles, thereby greatly improving the compaction density of the material and obtaining higher energy density in actual application.

[0040] Among them, regarding the halogen anion, it has higher electronegativity than the sulfate, phosphate, carbonate and other acid root ions commonly used in the art, and can form stronger bonding with the transition metal ions Mn and V originally in the positive electrode material, thereby more significantly improving the structural stability and electrochemical performance of the positive electrode material. The Li and / or K alkali cation has a more suitable ionic radius than other cations commonly used in the art, such as Ca 2+ , Mg 2+ , etc., and can more easily embed and de-embed in the polyanionic phosphate structure, thereby improving the charge and discharge performance of the secondary battery prepared by using the positive electrode material. At the same time, the above-mentioned ions also exhibit higher electrical conductivity to further optimize the electrochemical performance of the positive electrode material.

[0041] On the basis of the above types of anions and cations, the doping amount of the anions and cations is preferably 0.001≤x≤0.05, that is, the stoichiometric number in the positive electrode material is uniform and is 0.001≤x≤0.05, thereby more effectively adjusting the electronic structure, enhancing the migration of Na + ions and forming new active sites, so that the positive electrode material exhibits higher electrochemical performance.

[0042] In particular, in addition to the selection of the above-mentioned cation and anion types and the doping amount, more importantly, the coordination relationship between the two doping elements and the poly-anion phosphate positive electrode material substrate is more important. The poly-anion phosphate positive electrode material itself has a high theoretical specific capacity and good cycle stability, and when the above-mentioned cation and anion are introduced at a specific doping amount, the electrochemical performance can be further improved. Compared with other types of positive electrode active materials, such as olivine-type phosphates, the poly-anion phosphate involved in the present application has better compatibility and coordination with the above-mentioned cation and anion, and finally a positive electrode with better electrochemical performance can be obtained. Therefore, the doping of cation and anion can enhance the structural stability, improve the electrical conductivity, promote the ion migration, and thus improve the electrochemical performance of the positive electrode material. This synergistic effect makes the poly-anion phosphate positive electrode material have more significant advantages in performance.

[0043] In some embodiments, the molecular formula of the composite particle is Na4MxN(1-x)PO4, wherein 0.001≤x≤0.01; M is Li and / or K, and N is selected from one or more of F, Br and I.

[0044] In this embodiment, the molecular formula of the composite particle is Na4MxN(1-x)PO4, wherein 0.001≤x≤0.01, so as to better avoid the increase of the internal resistance of the positive electrode material and the decrease of the cycle stability due to the destruction of the structure of the positive electrode material. Meanwhile, it is preferred that M is Li and / or K, and N is selected from one or more of F, Br and I.

[0045] In some embodiments, it is preferred that the molecular formula of the composite particle is Na4MxN(1-x)PO4, wherein 0.001≤x≤0.01. 0.01 Mn 0.995 V(PO4) 2.997 N 0.01 , wherein M is Li and / or K, and N is selected from one or more of F, Br and I; or, the molecular formula of the composite particle is Na4MxN(1-x)PO4, wherein 0.001≤x≤0.01. 0.001 Mn 0.9995 V(PO4) 2.9997 N 0.001 , wherein M is Li and / or K, and N is F. Under the above-mentioned optimized molecular structure, the doped cation and anion can better coordinate with each other, and thus a positive electrode material with more superior electrochemical performance can be obtained.

[0046] In some embodiments, considering the changes in the molecular structure and electronic structure of the phosphate positive electrode material due to the doping of cation and anion, it is preferred that the molecular formula of the composite particle is Na4MxN(1-x)PO4, wherein 0.001≤x≤0.01. 0.01 Mn 0.995 V(PO4) 2.997 F 0.01 , Na4Li 0.01 Mn 0.995 V(PO4) 2.997 F 0.01 , Na4K0.01 Mn 0.995 V(PO4) 2.997 Br 0.01 , Na4K 0.01 Mn 0.995 V(PO4) 2.997 I 0.01 , Na4K 0.001 Mn 0.9995 V(PO4) 2.9997 F 0.001 or Na4K 0.05 Mn 0.975 V(PO4) 2.983 F 0.05 , and thus a positive electrode material with better electrochemical performance and better stability is obtained.

[0047] In addition, in order to further improve the stability and electrical conductivity of the positive electrode material, preferably, the positive electrode material further comprises a carbon coating layer coated on the outer surface of the composite particles, and the mass fraction of the carbon coating layer is 1% to 5% based on 100% of the total weight of the positive electrode material. More preferably, the mass fraction of the carbon coating layer is 2.0% to 2.5% based on 100% of the total weight of the positive electrode material.

[0048] The second aspect of the present application provides a preparation method of a positive electrode material, the preparation method comprising: preparing a mixed slurry of a sodium source, a doping element source, a manganese source, a vanadium source and a phosphorus source; and sequentially drying and calcining the mixed slurry to obtain the positive electrode material; wherein the positive electrode material comprises composite particles, and the molecular formula of the composite particles is Na4M x Mn 1-x / 2 V(PO4) 3-x / 3N x , 0.001≤x≤0.05; M is Li and / or K, and N is selected from one or more of F, Cl, Br and I.

[0049] For the above-mentioned positive electrode material, the present application correspondingly provides a preparation method thereof, which is simple to operate and easy to control, can optimize the reaction process to a greater extent, and can prepare the positive electrode material with excellent electrochemical performance at a lower manufacturing cost.

[0050] Further, in order to introduce a more uniform carbon layer on the surface of the positive electrode material to improve its electrical conductivity, the step of preparing the mixed slurry comprises: preparing a carbon source solution with a concentration of 0.18 mol / L to 0.20 mol / L, and adding the sodium source, the doping element source, the manganese source, the vanadium source and the phosphorus source into the carbon source solution to obtain the mixed slurry after stirring. At the same time, preferably, the carbon source is selected from one or more of glucose, citric acid monohydrate and soluble starch.

[0051] In some embodiments, the calcining comprises sequentially performing: a first-stage calcining at a temperature of 320-370 DEG C for 3-5 hours; and a second-stage calcining at a temperature of 700-750 DEG C for 7-9 hours. The present application refines the calcining process into two stages, thereby helping to better realize the doping of cations and anions, and also better inhibiting the deterioration of the structure of the polyanion-type phosphate positive electrode material itself, and enhancing the structural stability and electrochemical performance thereof.

[0052] In order to better protect the structure of the positive electrode material and reduce the introduction and generation of impurities, the first-stage calcining and the second-stage calcining are both performed under the protection of an inert gas, and more preferably the inert gas is argon and / or nitrogen, so that the positive electrode material has higher electrochemical performance and better stability, and the specific capacity and long cycle stability of the sodium ion battery prepared therefrom are higher.

[0053] Further, in order to more quickly and uniformly remove moisture, reduce material agglomeration, and optimize the microstructure and density of the positive electrode material, the drying is spray drying, and the inlet temperature of the spray drying is 200-250 DEG C and the outlet temperature is 100-140 DEG C.

[0054] In some embodiments, the doping element source is selected from one or more of potassium fluoride, lithium fluoride, potassium bromide, and potassium iodide. The above-mentioned doping element source can more significantly optimize the molecular structure and electronic structure of the positive electrode material, and does not introduce other impurity elements, so as to more effectively improve the electrochemical performance and structural stability of the positive electrode material.

[0055] Further, the sodium source is selected from one or more of sodium acetate, sodium carbonate, sodium hydroxide, and sodium nitrate; and / or, the phosphorus source is selected from one or more of ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, ammonium phosphate, and phosphoric acid. The selection of the sodium source and the phosphorus source has an important influence on the synthesis process and the final performance of the positive electrode material, and by adjusting the types thereof as above, the synthesis conditions of the positive electrode material can be optimized, and the consistency and stability of the material can be improved.

[0056] Further, the manganese source is selected from one or more of manganese acetate tetrahydrate, manganese nitrate, manganese phosphate, and manganese oxalate; and / or, the vanadium source is selected from one or more of ammonium metavanadate, ammonium vanadate, and ammonium sulfate. The selection of the manganese source and the vanadium source can affect the electronic structure and ion diffusion path of the positive electrode material, and by optimizing the two thereof as above, the electronic conductivity and ion diffusion efficiency of the positive electrode material can be further improved.

[0057] A third aspect of the present application provides a positive electrode tab, which comprises the above-mentioned positive electrode material, or a positive electrode material prepared by the preparation method of the above-mentioned positive electrode material.

[0058] The positive electrode material provided by the application has excellent electrochemical performance and stability, so when used as an active material of a positive electrode sheet, the corresponding positive electrode sheet also has high energy density, long cycle life and excellent electrochemical stability, thereby significantly improving the overall performance of the battery.

[0059] The fourth aspect of the application provides a sodium ion battery comprising the positive electrode sheet.

[0060] The positive electrode sheet provided by the application has high energy density and long cycle life due to the presence of the positive electrode material with excellent electrochemical performance, so when the positive electrode sheet is applied to a sodium ion battery, the sodium ion battery also has high discharge specific capacity and long cycle stability.

[0061] The application will be further described in detail below in combination with specific examples, which cannot be understood as limiting the scope of the application.

[0062] Unless otherwise defined, all professional terms used below have the same meaning as generally understood by those skilled in the art. The professional terms used in the present application are only for the purpose of describing specific examples and are not intended to limit the protection scope of the application.

[0063] Some specific examples are listed below, and it should be noted that the examples described below are exemplary and are only used to explain the application and cannot be understood as limiting the application. If the specific technology or conditions are not specified in the examples, the technology or conditions described in the literature in the art or according to the product manual are used. If the reagents or instruments are not specified by the manufacturer, they are all conventional products that can be obtained by purchase.

[0064] I. Preparation method

[0065] Example 1

[0066] A preparation method of a positive electrode material:

[0067] Citric acid monohydrate (C6H8O7·H2O) was weighed and added to deionized water to prepare a transparent solution with a C6H8O7·H2O concentration of 0.18 mol / L.

[0068] Sodium source sodium acetate (CH3COONa), doping element source potassium fluoride (KF), manganese source manganese acetate tetrahydrate [(CH3COO)2Mn·4H2O], vanadium source ammonium metavanadate (NH4VO3) and phosphorus source ammonium dihydrogen phosphate (NH4H2PO4) were weighed according to the molar ratio of 4:0.001:0.9995:1:2.9997 and sequentially added to the above solution, and then the solution was continuously stirred to obtain a mixed slurry.

[0069] The mixed slurry is spray-dried to obtain a brownish yellow precursor material, and the spray-drying process is carried out at an inlet temperature of 220°C and an outlet temperature of 120°C; the brownish yellow precursor material is placed in a sintering furnace in an argon atmosphere, heated to 350°C at a heating rate of 5°C / min and kept at this temperature for 4h, i.e. first-stage calcination, then heated to 720°C at a heating rate of 5°C / min and kept at this temperature for 8h, i.e. second-stage calcination, to complete sintering. 1

[0070] After sintering, a black powder is obtained, which is a carbon-coated K+and F- co-doped Na4MnV(PO4)3 material, and the molecular formula is Na4K 0.001 Mn 0.9995 V(PO4) 2.9997 F 0.001 . Meanwhile, the mass fraction of the carbon-coated layer is 2.4% based on the total weight of the black powder.

[0071] The XRD pattern of the obtained positive electrode material is shown in Figure 1 , and the SEM characterization results are shown in Figure 2 (a) and Figure 2 (b), wherein Figure 2 the scale in (a) is 15μm, Figure 2 and the scale in (b) is 5μm.

[0072] As can be seen from Figure 1 , the positive electrode material doped with K and F ions obtained in Example 1 still has a crystal form consistent with that of undoped Na4MnV(PO4)3. That is to say, after K+and F- co-doping, the crystal form of the obtained positive electrode material is not destroyed, and it is still a poly-anion type phosphate structure, and the corresponding structural advantages are also retained, so that it can exhibit more superior electrochemical performance on this basis.

[0073] Example 2

[0074] A method for preparing a positive electrode material:

[0075] The difference between this example and Example 1 is only that the molar ratio of the sodium source sodium acetate (CH3COONa), the doping element source potassium fluoride (KF), the manganese source manganese acetate tetrahydrate [(CH3COO)2Mn·4H2O], the vanadium source ammonium metavanadate (NH4VO3) and the phosphorus source ammonium dihydrogen phosphate (NH4H2PO4) is changed to 4:0.01:0.995:1:2.997.

[0076] A black powder is obtained, which is a carbon-coated K+and F- co-doped Na4MnV(PO4)3 material, and the molecular formula is Na4K 0.01 Mn 0.995 V(PO4) 2.997 ​F 0.01 .

[0077] Example 3

[0078] A preparation method of a positive electrode material:

[0079] The difference between this example and Example 1 is only that the molar ratio of the sodium source sodium acetate (CH3COONa), the doping element source potassium fluoride (KF), the manganese source manganese acetate tetrahydrate [(CH3COO)2Mn·4H2O], the vanadium source ammonium metavanadate (NH4VO3), and the phosphorus source ammonium dihydrogen phosphate (NH4H2PO4) is changed to 4:0.05:0.975:1:2.983.

[0080] A black powder, that is, a carbon-coated K+and F-co-doped Na4MnV(PO4)3 material, is obtained, and the molecular formula is Na4K 0.04 Mn 0.975 V(PO4) 2.983 F 0.05 .

[0081] Example 4

[0082] A preparation method of a positive electrode material:

[0083] The difference between this example and Example 2 is only that equimolar lithium fluoride (LiF) is used to replace potassium fluoride (KF), and a carbon-coated Li + and F - -co-doped Na4MnV(PO4)3 material is obtained, and the molecular formula is Na4Li 0.01 Mn 0.995 V(PO4) 2.997 F 0.01 .

[0084] Example 5

[0085] A preparation method of a positive electrode material:

[0086] The difference between this example and Example 2 is only that equimolar potassium bromide (KBr) is used to replace potassium fluoride (KF), and a carbon-coated K+and Br-co-doped Na4MnV(PO4)3 material is obtained, and the molecular formula is Na4K 0.01 Mn 0.995 V(PO4) 2.997 Br 0.01 .

[0087] Example 6

[0088] A preparation method of a positive electrode material:

[0089] The difference between this embodiment and embodiment 2 is only that equimolar amount of potassium iodide (KI) is used to replace potassium fluoride (KF) to obtain carbon-coated K + and I - The synergistically doped Na4MnV(PO4)3 material has a molecular formula of Na4K 0.01 Mn 0.995 V(PO4) 2.997 I 0.01 .

[0090] Embodiment 7

[0091] A preparation method of a positive electrode material:

[0092] The difference between this embodiment and embodiment 1 is only that the inlet air temperature in the spray drying process is changed to 280℃ and the outlet air temperature is changed to 80℃.

[0093] Embodiment 8

[0094] A preparation method of a positive electrode material:

[0095] The difference between this embodiment and embodiment 1 is only that the inlet air temperature in the spray drying process is changed to 180℃ and the outlet air temperature is changed to 160℃.

[0096] Embodiment 9

[0097] A preparation method of a positive electrode material:

[0098] The difference between this embodiment and embodiment 1 is only that the temperature of the first-stage calcination is changed to 320℃ and the holding time is changed to 5h; the temperature of the second-stage calcination is changed to 700℃ and the holding time is changed to 9h.

[0099] Embodiment 10

[0100] A preparation method of a positive electrode material:

[0101] The difference between this embodiment and embodiment 1 is only that the temperature of the first-stage calcination is changed to 370℃ and the holding time is changed to 3h; the temperature of the second-stage calcination is changed to 750℃ and the holding time is changed to 7h.

[0102] Embodiment 11

[0103] A preparation method of a positive electrode material:

[0104] The difference between this embodiment and embodiment 1 is only that the temperature of the first-stage calcination is changed to 300℃ and the holding time is changed to 6h; the temperature of the second-stage calcination is changed to 780℃ and the holding time is changed to 6h.

[0105] Embodiment 12

[0106] A preparation method of a positive electrode material

[0107] The difference between this example and example 1 is that the temperature of the first-stage calcination is changed to 400℃, and the holding time is changed to 2h; the temperature of the second-stage calcination is changed to 680℃, and the holding time is changed to 10h.

[0108] Example 13

[0109] A preparation method of a positive electrode material

[0110] The difference between this example and example 1 is that the second-stage calcination is not performed, and the sintering furnace used for calcination is not protected by argon atmosphere.

[0111] Comparative example 1

[0112] A preparation method of a positive electrode material

[0113] The difference between this comparative example and example 1 is that the doping element source KF is not added, and the molar ratio of the sodium source sodium acetate (CH3COONa), the doping element source potassium fluoride (KF), the manganese source manganese acetate tetrahydrate [(CH3COO)2Mn·4H2O], the vanadium source ammonium metavanadate (NH4VO3) and the phosphorus source ammonium dihydrogen phosphate (NH4H2PO4) is changed to 4:1:1:3.

[0114] The obtained black powder is a carbon-coated undoped Na4MnV(PO4)3 material.

[0115] The XRD pattern of the obtained positive electrode material is shown in Figure 1 , and the SEM characterization results are shown in Figure 2 (c) and Figure 2 (d), wherein Figure 2 The scale in (c) is 15μm, Figure 2 The scale in (d) is 5μm.

[0116] Comparative example 2

[0117] A preparation method of a positive electrode material

[0118] The difference between this comparative example and example 1 is that the molar ratio of the sodium source sodium acetate (CH3COONa), the doping element source potassium fluoride (KF), the manganese source manganese acetate tetrahydrate [(CH3COO)2Mn·4H2O], the vanadium source ammonium metavanadate (NH4VO3) and the phosphorus source ammonium dihydrogen phosphate (NH4H2PO4) is changed to 4:0.0005:0.99975:1:2.9998, obtaining K + and F - co-doped Na4MnV(PO4)3 material, and the molecular formula is Na4K 0.0005 Mn 0.99975 V(PO4) 2.9998F 0.0005 .

[0119] Comparative Example 3

[0120] A preparation method of a positive electrode material:

[0121] The difference between this comparative example and Example 1 is only that the molar ratio of the sodium source sodium acetate (CH3COONa), the doping element source potassium fluoride (KF), the manganese source manganese acetate tetrahydrate [(CH3COO)2Mn·4H2O], the vanadium source ammonium metavanadate (NH4VO3), and the phosphorus source ammonium dihydrogen phosphate (NH4H2PO4) is changed to 4:0.1:0.95:1:2.97, obtaining K + and F - The synergistically doped Na4MnV(PO4)3 material has a molecular formula of Na4K 0.1 Mn 0.95 V(PO4) 2.97 F 0.1 .

[0122] Comparative Example 4

[0123] A preparation method of a positive electrode material:

[0124] The difference between this comparative example and Example 1 is only that an equal molar amount of potassium sulfate (K2(SO4)) is used to replace potassium fluoride (KF), obtaining carbon-coated K + and SO4 2- The synergistically doped Na4MnV(PO4)3 material has a molecular formula of Na4K 0.001 Mn 0.9995 V(PO4) 2.9997 (SO4) 0.0005 .

[0125] Comparative Example 5

[0126] A preparation method of a positive electrode material:

[0127] The difference between this comparative example and Example 1 is only that an equal molar amount of calcium fluoride (CaF2) is used to replace potassium fluoride (KF), obtaining carbon-coated Ca 2+ and F - The synergistically doped Na4MnV(PO4)3 material has a molecular formula of Na4Ca 0.001 Mn 0.9995 V(PO4) 2.997 F 0.002 .

[0128] II. Test method

[0129] Compacted density: The compacted density of the powder of the positive electrode material obtained in each example and comparative example is determined according to GB / T 24533.

[0130] Battery preparation and performance test: the positive material, Super P (conductive additive) and binder (PVDF + NMP) are ground and mixed in a mass ratio of 7:2:1, and then the uniformly mixed slurry is uniformly coated on a dry aluminum foil with a square container (coater). The coated slurry is dried in a vacuum oven at 100°C for 12h, and after cooling to room temperature, it is cut into a circular electrode sheet with a 12mm mold, and then the mass of the electrode sheet is weighed with an electronic balance, and the average value of three times is taken, and finally it is placed in a 100°C drying oven for storage. The process of assembling the battery is carried out in an argon atmosphere glove box. The prepared electrode sheet is placed in the overstock bin of the glove box, vacuumized and gassed repeatedly three times, then taken into the glove box, and the sodium block is cut and flattened with a 12mm mold to form a circular sodium sheet. Then the gasket and sodium sheet are placed in the negative electrode shell in turn and flattened, and then the separator is placed in it, and the electrolyte is added dropwise, and the electrode sheet (the positive material side faces the separator) is placed, and then the gasket and spring sheet are placed, and the positive electrode shell is buckled to form a CR2032 button cell. Finally, it is sealed on the battery sealing machine, and after standing at room temperature for about 6h, it is subjected to electrochemical test. The electrolyte is a mixture of 1M NaClO4 and 95%PC and 5%FEC, and the separator is glass fiber. The battery samples corresponding to the positive electrode materials prepared in each example and comparative example are obtained, and each battery sample is subjected to charge and discharge at 2.5V-3.8V at 25°C. The discharge specific capacity at 0.1C and 1C is tested respectively. The cycle performance is tested by a new Wei electrochemical test cabinet, and the specific capacity reduction rate after 500 cycles at 1C is obtained.

[0131] The above test results are shown in Table 1.

[0132] Table 1

[0133]

[0134]

[0135] III. Analysis of test results of each example and comparative example

[0136] From the above results, it can be seen that the above-mentioned examples of the present application achieve the preparation of a positive electrode material with excellent electrochemical performance. Specifically:

[0137] Comparing each example with the comparative example, it can be seen that the Na4Mn x Mn 1-x / 2 V(PO4) 3-x / 3 N xThe composite particle has a molecular formula of Na4M

[0138] Comparing Example 3 with Example 1, Example 2, Example 4, Example 5 and Example 6, it can be seen that, in addition to the selection of anion and cation species, the amount of doping in coordination with the species also has an effect on the performance of the resulting positive electrode material. From these examples, it can be seen that, when the composite particle has a molecular formula of Na4M 0.01 Mn 0.995 V(PO4) 2.997 N 0.01 , M is Li and / or K, and N is selected from one or more of F, Br and I, the resulting positive electrode material exhibits more superior electrochemical performance. When the composite particle has a molecular formula of Na4M 0.001 Mn 0.9995 V(PO4) 2.9997 N 0.001 , M is Li and / or K, and N is F, the resulting positive electrode material exhibits more superior electrochemical performance. When the composite particle has a molecular formula of Na4K 0.01 Mn 0.995 V(PO4) 2.997 F 0.01 , Na4Li 0.01 Mn 0.995 V(PO4) 2.997 F 0.01 , Na4K 0.01 Mn 0.995 V(PO4) 2.997 Br 0.01 , Na4K 0.01 Mn 0.995 V(PO4) 2.997 I 0.01 , Na4K 0.001 Mn 0.9995 V(PO4) 2.9997 F 0.001 or Na4K 0.05 Mn 0.975 V(PO4) 2.983 F 0.05 , the resulting positive electrode material has a higher specific capacity and better cycle stability when a battery is prepared therefrom.

[0139] Comparing example 7, example 8 with example 1, it can be seen that when the drying is spray drying, and the inlet temperature of the spray drying is 200-250℃, and the outlet temperature is 100-140℃, the material aggregation can be reduced, the microstructure and density of the positive material can be optimized, and the positive material exhibits higher electrochemical performance.

[0140] Comparing example 9, example 10 with example 1, example 11 and example 12, it can be seen that the temperature of the first stage calcination is preferably 320-370℃, and the holding time is preferably 3-5h. At the same time, the temperature of the second stage calcination is preferably 700-750℃, and the holding time is preferably 7-9h, which helps to better realize the doping of anions and cations. This calcination temperature can also better inhibit the deterioration of the structure of the poly-anion phosphate positive material itself, and enhance the structural stability and electrochemical performance.

[0141] Comparing example 13 with example 1, it can be seen that the calcination process is divided into two stages, and the first stage calcination and the second stage calcination are both carried out under the protection of inert gas, which can obtain a positive material with higher electrochemical performance and better stability, and finally make the specific capacity and long cycle stability of the prepared sodium ion battery higher.

[0142] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications of the embodiments that can be thought of by those skilled in the art, and other ways constructed by combining part of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode material, characterized by, The positive electrode material comprises composite particles, the molecular formula of the composite particles is Na4M x Mn 1-x / 2 V(PO4) 3-x / 3 N x wherein 0.001≤x≤0.05; M is Li and / or K, and N is selected from one or more of F, Cl, Br and I.

2. The positive electrode material according to claim 1, characterized in that, In the molecular formula of the composite particle, 0.001≤x≤0.01; M is Li and / or K, and N is selected from one or more of F, Br and I.

3. The positive electrode material of claim 2, wherein, The molecular formula of the composite particle is Na4M 0.01 Mn 0.995 V(PO4) 2.997 N 0.01 wherein M is Li and / or K, and N is selected from one or more of F, Br, and I. or, the molecular formula of the composite particle is Na4M 0.001 Mn 0.9995 V(PO4) 2.9997 N 0.001 wherein M is Li and / or K, and N is F.

4. The positive electrode material according to claim 3, characterized in that, The molecular formula of the composite particle is Na4K 0.01 Mn 0.995 V(PO4) 2.997 F 0.01 , Na4Li 0.01 Mn 0.995 V(PO4) 2.997 F 0.01 , Na4K 0.01 Mn 0.995 V(PO4) 2.997 Br 0.01 , Na4K 0.01 Mn 0.995 V(PO4) 2.997 I 0.01 , Na4K 0.001 Mn 0.9995 V(PO4) 2.9997 F 0.001 , or Na4K 0.05 Mn 0.975 V(PO4) 2.983 F 0.05 .

5. A method for producing a positive electrode material, characterized by, The preparation method of the positive electrode material comprises: a sodium source, a doping element source, a manganese source, a vanadium source and a phosphorus source are prepared into a mixed slurry; the mixed slurry is sequentially subjected to drying and calcination to obtain the positive electrode material; The positive electrode material comprises composite particles, and a molecular formula of the composite particles is Na4M x Mn 1-x / 2 V(PO4) 3-x / 3 N x wherein 0.001≤x≤0.05; M is Li and / or K, and N is selected from one or more of F, Cl, Br and I.

6. The method for preparing the cathode material according to claim 5, characterized in that, the calcination comprises sequentially performing: first-stage calcination at a temperature of 320-370 DEG C for 3-5 h; second-stage calcination at a temperature of 700-750 DEG C for 7-9 h.

7. The method for preparing the cathode material according to claim 6, characterized in that, The drying is spray drying, and the inlet temperature of the spray drying is 200-250 DEG C, and the outlet temperature is 100-140 DEG C.

8. The preparation method of the positive electrode material of claim 7, wherein, the doping element source is selected from one or more of potassium fluoride, lithium fluoride, potassium bromide and potassium iodide; and / or, the sodium source is selected from one or more of sodium acetate, sodium carbonate, sodium hydroxide and sodium nitrate; and / or, the manganese source is selected from one or more of manganese acetate tetrahydrate, manganese nitrate, manganese phosphate and manganese oxalate; and / or, the vanadium source is selected from one or more of ammonium metavanadate, ammonium vanadate and ammonium sulfate; and / or, the phosphorus source is selected from one or more of ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, ammonium phosphate and phosphoric acid.

9. A positive electrode sheet characterized by comprising: The positive electrode tab comprises the positive electrode material of any one of claims 1-4, or the positive electrode material prepared by the preparation method of any one of claims 5-8.

10. A sodium-ion battery, characterized in that, The positive electrode tab as claimed in claim 9 is included.

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